Salts of Laked Monoazo Compounds

ABSTRACT

The present invention relates to monoazo compounds of formula (I) which are present in the form of mono-, di-, tri- or tetra-valent mixed salts of different cations, such as, for example, Ca 2+ , Na + , NH 4   + , NR 4   + , H + , Li + , K + , Mg 2+ , Ba 2+ , Sr 2+ , AI 2+ , Pb 2+ , Mn 2+ , Zn 2+ , Cr 2+ , Co 2+ , Fe 2+ , Fe 3+ , Zr 4+  and CU 2+ , R being C 2 -C 6 alkyl, in freely selected ratios, and to the calcium salt of the monoazo compound of formula (I) which has two crystal polymorph forms—a reddish yellow and a greenish yellow—having different properties, for example colour shade or high-temperature stability, to the preparation of such compounds and to their use in the mass-pigmenting of organic materials and in the production of wax transfer ribbons, toners or colour filters.

The present invention relates to novel monoazo compounds, to processes for their preparation and to their use as colorants, especially in the colouring of high molecular weight material.

A large number of monoazo compounds that can be used as pigments are known. The increasingly high demands being made of the quality of colorations, for example the fastness properties, or the performance properties, for example the oversprayability, have resulted in there being a continuing need for new pigments having improved properties, especially in respect of fastness properties.

The aim of the present invention is therefore to provide novel, improved pigments based on monoazo compounds that can be used especially in the production of surface coatings, printing inks and colour filters or in the colouring of plastics. The novel pigments should yield colorations having high purity of shade, high colour strength and good fastness to overspraying.

It has been found that the desired aim is substantially achieved by the novel monoazo compounds defined hereinbelow.

The present invention accordingly relates to a monoazo compound of formula

which is present in the form of a mono-, di-, tri- or tetra-valent mixed salt of different cations, such as, for example, Ca²⁺, Na⁺, NH₄ ⁺, NR₄ ⁺, H⁺, Li⁺, K⁺, Mg²⁺, Ba²⁺, Sr²⁺, Al³⁺, Pb²⁺, Mn²⁺, Zn²⁺, Cr²⁺, Co²⁺, Fe²⁺, Fe³⁺, Zr⁴⁺ and Cu²⁺ wherein R is C₁-C₆alkyl, in a freely selected ratio, and to the calcium salt of the monoazo compound of formula (1) which has two crystal polymorph forms—a somewhat reddish yellow (α-modification) and a greenish yellow (β-modification)—having different properties, for example colour shade or high-temperature stability.

R as C₁-C₆alkyl is e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl or hexyl.

Preferred as R is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, especially ethyl and more especially methyl.

The mixed salts according to the invention may be in the form of ternary salts, e.g. in the form of Ca⁺⁺/NH₄ ⁺/Na⁺ or Ca⁺⁺/K⁺/Na⁺ mixed salts.

The mixed salts according to the invention preferably contain two different cations. In a mixed salt containing two cations, the ratio of the cations may vary within a wide range, e.g. from 99.5 to 0.5 mol % of one cation to from 0.5 to 99.5 mol % of the other cation, preferably from 80 to 20 mol % of one cation to from 20 to 80 mol % of the other cation, more especially from 60 to 40 mol % of one cation to from 40 to 60 mol % of the other cation.

Preference is given to the monoazo compound of formula (1) present in the form of a Ca²⁺/Na⁺ mixed salt, or especially a Ca²⁺/NH₄ ⁺ or Ca²⁺/K⁺ mixed salt.

Of those mixed salts, preference is given to those having a Ca²⁺ content of >50 mol %, based on the total molar amount of the cations.

Of importance are Ca²⁺/NH₄₊ mixed salts that have a NH₄ ⁺ content of from 5 to 50 mol %, especially from 8 to 30 mol %, more especially from 10 to 30 mol %, based on the total molar amount of cations in the form of mixed crystals.

Also of importance are Ca²⁺/K⁺ mixed salts that have a K⁺ content of from 5 to 50 mol %, especially from 8 to 30 mol %, more especially from 10 to 30 mol %, based on the total molar amount of cations in the form of mixed crystals.

Of the two crystal polymorphs of the Ca²⁺ salt of the compound of formula (1), the greenish β-modification, which has better high-temperature stability and all-round fastness properties, is preferred.

The β-modification is formed predominantly at relatively high temperatures (>50° C.).

The present invention relates also to a process for the preparation of the monoazo compounds of formula (1) according to the invention.

They are prepared, for example, by diazotisation of 2-amino-5-nitrobenzenesulfonic acid or a salt or a mixed salt thereof, and coupling to 3-acetoacetylamino-4-methoxy-benzenesulfonic acid/salt.

The monoazo compounds of formula (1) according to the invention exhibit substantially better fastness properties than similar known products and are therefore excellently suitable as tinctorially strong and high-temperature-stable pigments.

The monoazo compounds of formula (1) according to the invention are distinguished especially by high fastness to migration, to water and to solvents, stability to light, to weathering and to high temperatures, good rheology and ready dispersibility, those advantageous properties being achievable, wholly unexpectedly and in contrast to products known hitherto, also in combination with high colour strength. The colour saturation (chroma C*) is also astonishingly high.

The monoazo compounds of formula (1) according to the invention exhibit outstanding crystallinity. Nevertheless, they may optionally be subjected to additional after-treatment in order to optimise their properties still further. That step may be carried out according to processes known per se, for example by heating in water, a slightly polar hydrophilic organic solvent or a mixture thereof, to a temperature of approximately from 50 to 200° C. (optionally under pressure) for a period that may be from a few minutes up to 100 hours depending on the recrystallising medium and the temperature. Preference is given to after-treatment in water for from 0.5 to 6 hours at from 50 to 99° C., especially for from 1 to 4 hours at from 65 to 85° C. After-treatment is preferably carried out directly after laking, optionally without intermediate isolation.

The monoazo compounds of formula (1) according to the invention can be isolated in pure form and dried, following which they are readily dispersible in plastics, surface coatings and printing inks, for example by means of a ball mill or bead mill. They can also be used in the form of moist press cakes, without further processing, for the preparation of pigment dispersions. Conventional additives in conventional concentrations may be added to the monoazo compounds of formula (1) according to the invention, as required, before or during precipitation or isolation in order to improve the application-related properties.

As well as being suitable for the mass-pigmenting of high molecular weight organic materials in the form of plastics, surface coatings and printing inks, the monoazo compounds of formula (1) according to the invention are also suitable, for example, for the production of solid toners, wax transfer ribbons or colour filters.

The high molecular weight organic material to be coloured according to the invention may be of natural or synthetic origin and usually has a molecular weight in the range of from 10³ to 10⁸ g/mol. It may be, for example, a natural resin or drying oil, rubber or casein, or a modified natural material such as chlorinated rubber, an oil-modified alkyd resin, viscose, a cellulose ether or ester, such as cellulose acetate, cellulose propionate, cellulose acetobutyrate or nitrocellulose, but especially a totally synthetic organic polymer (both thermosetting plastics and thermoplastics), as obtained by polymerisation, polycondensation or polyaddition, for example a polyolefin, such as polyethylene, polypropylene or polyisobutylene, a substituted polyolefin, such as a polymerisation product of vinyl chloride, vinyl acetate, styrene, acrylonitrile, an acrylic acid and/or methacrylic acid ester or butadiene, as well as a copolymer of the mentioned monomers, especially ABS or EVA.

From the series of the polyaddition resins and polycondensation resins there may be mentioned the condensation products of formaldehyde with phenols, so-called phenoplasts, and the condensation products of formaldehyde with urea, thiourea and melamine, so-called aminoplasts, the polyesters used as surface-coating resins, either saturated, such as alkyd resins, or unsaturated, such as maleic resins, and also linear polyesters and polyamides or silicones.

The mentioned high molecular weight compounds may be in the form of single compounds or mixtures, in the form of plastic masses or melts, which may optionally be spun to form fibres.

They may also be in the form of their monomers or in the polymerised state in dissolved form as film formers or binders for surface coatings or printing inks, such as boiled linseed oil, nitrocellulose, alkyd resins, melamine resins, urea-formaldehyde resins or acrylic resins.

The pigmenting of the high molecular weight organic substances with the monoazo compounds of formula (1) according to the invention is carried out, for example, by admixing such a monoazo compound, optionally in the form of a masterbatch, with the substrates using roll mills or mixing or grinding apparatus. The pigmented material is then generally brought into the desired final form by methods known per se, such as calendering, compression moulding, extrusion, coating, casting or by injection moulding. In order to produce non-rigid mouldings or to reduce their brittleness it is often desirable to incorporate so-called plasticisers into the high molecular weight compounds prior to shaping. As plasticisers there may be used, for example, esters of phosphoric acid, phthalic acid or sebacic acid. In the process according to the invention, the plasticisers may be incorporated into the polymers before or after the incorporation of the monoazo compound of formula (1) according to the invention. It is also possible, in order to achieve different shades, to add to the high molecular weight organic materials, in addition to the pigment compositions, also fillers or other colour-imparting constituents, such as white, coloured or black pigments as well as effect pigments, in each case in the desired amount.

For the pigmenting of surface coatings and printing inks, the high molecular weight organic materials and the monoazo compounds of formula (1) according to the invention are finely dispersed or dissolved, optionally together with additives such as fillers, other pigments, siccatives or plasticisers, generally in an organic and/or aqueous solvent or solvent mixture. It is possible to use a procedure in which the individual components are dispersed or dissolved separately or in which a plurality thereof are dispersed or dissolved together and only then all of the components combined.

Accordingly, a further embodiment relates to mass-coloured high molecular weight organic material, comprising

-   -   (a) from 0.05 to 70% by weight, based on the sum of (a) and (b),         of a monoazo compound of formula (1) according to the invention,         and     -   (b) from 99.95 to 30% by weight, based on the sum of (a) and         (b), of a high molecular weight organic material.

The material in question may be either a ready-for-use composition or an article formed therefrom, or a masterbatch, for example in the form of granules. The high molecular weight organic material coloured according to the invention may also comprise conventional additives, for example stabilisers.

Accordingly, a further embodiment relates to a method of mass-colouring high molecular weight organic material, which method comprises incorporating into such material a monoazo compound of formula (1) according to the invention, for example by mixing and processing the high molecular weight organic material together with the pigment composition according to the invention, optionally in the form of a masterbatch, in a manner known per se.

The Examples which follow serve to illustrate the invention. Unless otherwise indicated, parts are parts by weight and percentages are percent by weight. Temperatures are given in degrees Celsius. The relationship between parts by weight and parts by volume is the same as that between grams and cubic centimetres.

EXAMPLE 1

Preparation of the diazonium: 15.25 g (60 mmol, 92.5%) of 2-amino-5-nitrobenzene-sulfonic acid sodium/ammonium salt are stirred in 250 ml of deionised water, and 21 ml of a 37% HCl solution are added thereto. The resulting suspension is then cooled to a temperature of 0-5° C. by means of an ice bath, and 15 ml of a 4N sodium nitrite solution are added dropwise thereto. After 2 hours, 1 ml of 1N sulfamic acid is added.

Coupling: 18.55 g (60 mmol) of 3-acetoacetylamino-4-methoxybenzenesulfonic acid sodium salt are dissolved in 200 ml of deionised water; the resulting solution is then cooled to a temperature of 0-5° C. and the above diazonium suspension is added dropwise thereto, the pH being maintained at 4.5 by means of a 30% sodium hydroxide solution. When the addition is complete, the reaction mixture is stirred at room temperature for 2 hours. The resulting yellow suspension is then divided into three 230 g portions.

1.1) The first 230 g portion of the above yellow suspension is adjusted to pH 8 with a 30% sodium hydroxide solution, and a solution of 2.5 g of calcium chloride (Fluka purum) in 15 ml of deionised water is added thereto. The mixture is stirred at room temperature for 12 hours. The yellow suspension is then filtered through hard filters, washed with 200 ml of deionised water and dried in vacuo at 90° C. 9.94 g of the calcium salt of the compound of formula (1), which contains a little water, are obtained, which colours PVC plastics in yellow shades.

The complete X-ray diffraction diagram was determined by customary methods with the aid of a Siemens D500 X-ray diffractometer (CuKα radiation).

The X-ray diffraction diagram corresponds to the α-modification and is distinguished by the following diffraction lines: Lattice Angle 2 theta Relative intensity spacings (d values in angstrom) 10.93 81 8.09 13.85 45 6.39 14.66 56 6.04 16.50 46 5.37 17.10 29 5.18 19.67 88 4.51 19.98 44 4.44 21.98 25 4.04 22.64 18 3.92 24.83 26 3.58 26.97 100 3.30 28.18 30 3.16

1.2) The second 230 g portion of the above yellow suspension is heated to a temperature of 40° C.; the pH is adjusted to 8 by means of a 30% sodium hydroxide solution, and a solution of 2.5 g of calcium chloride (Fluka purum) in 15 ml of deionised water is added thereto. The mixture is then stirred for 2 hours at a temperature of 40° C. The yellow suspension is then filtered through hard filters, washed with 200 ml of deionised water and dried in vacuo at 90° C. 9.94 g of the calcium salt of the compound of formula (1), which contains a little water, are obtained, which colours PVC plastics in yellow shades.

The X-ray diffraction diagram of the resulting compound corresponds to the α-modification (see Point 1).

1.3) The third 230 g portion of the above yellow suspension is heated to 60° C.; the pH is adjusted to 8 with a 30% sodium hydroxide solution, and a solution of 2.5 g of calcium chloride (Fluka purum) in 15 ml of deionised water is added thereto. The mixture is then stirred for 2 hours at a temperature of 60° C. The yellow suspension is then filtered through hard filters, washed with 200 ml of deionised water and dried in vacuo at 90° C. 9.99 g of the calcium salt of the compound of formula (1), which contains a little water, are obtained, which colours PVC plastics in greenish-yellow shades.

The complete X-ray diffraction diagram was determined by customary methods with the aid of a Siemens D500 X-ray diffractometer (CuKα radiation).

The X-ray diffraction diagram of the resulting compound corresponds to the β-modification and is distinguished by the following diffraction lines: Lattice Angle 2 theta Relative intensity spacings (d values in angstrom) 4.63 100 19.05 9.40 12 9.41 14.18 28 6.24 18.30 20 4.84 21.61 18 4.11 21.87 10 4.06 23.46 15 3.79 24.78 11 3.59 26.30 14 3.39 26.69 34 3.34 26.98 46 3.30

EXAMPLE 1.4

Preparation of the diazonium: 5.89 g (20 mmol, 82%) of 2-amino-5-nitrobenzene-sulfonic acid sodium salt are stirred in 80 ml of deionised water, and 7 ml of an aqueous 37% HCl solution are added thereto. The suspension is then cooled to a temperature of 0-5° C. by means of an ice bath, and 5 ml of a 4N sodium nitrite solution are added dropwise thereto. After 2 hours, 1 ml of an aqueous 1N sulfamic acid solution is added.

Coupling: 6.18 g (20 mmol) of 3-acetoacetylamino-4-methoxybenzenesulfonic acid sodium salt are dissolved in 60 ml of deionised water. The solution is cooled to a temperature of 0-5° C. and the above diazonium suspension is added dropwise thereto, the pH being maintained at 4.5-5.0 by means of a 30% sodium hydroxide solution. When the addition is complete, the reaction mixture is stirred at 2° C. for 1.5 hours and then at room temperature for 12 hours. The yellow suspension is then heated to 60° C. by means of an oil bath; a solution of 2.5 g of calcium chloride in 15 ml of deionised water is added and stirring is then carried out for 2 hours. The resulting yellow suspension is filtered by means of hard filters, washed with 1 litre of hot water and dried in a vacuum cabinet at 90° C. 9.7 g of the calcium salt of the compound of formula (1), which contains a little water, are obtained, which colours PVC plastics in yellow shades.

The X-ray diffraction diagram of the resulting compound corresponds to the α-modification (see Example 1.3).

EXAMPLE 2

Preparation of the diazonium: 5.0 g (20 mmol, 92.5%) of 2-amino-5-nitrobenzenesulfonic acid sodium/ammonium salt are stirred in 100 ml of deionised water, and 7 ml of a 37% HCl solution are added. The suspension is then cooled to a temperature of 0-5° C. by means of an ice bath, and 5 ml of a 4N sodium nitrite solution are added dropwise thereto. After 2 hours, 0.5 ml of 1N sulfamic acid is added.

Coupling: 6.2 g (20 mmol) of 3-acetoacetylamino-4-methoxybenzenesulfonic acid sodium salt are dissolved in 200 ml of deionised water, and 5 ml of a 30% sodium hydroxide solution are added. The resulting solution is then added dropwise to the above diazonium suspension until a pH of 4.5-5.0 is obtained, the pH thereafter being maintained in that range by means of a 37% HCl solution. When the addition is complete, the reaction mixture is stirred for a further 2 hours at room temperature, then heated to a temperature of 70° C. and adjusted to pH 8 with a 30% sodium hydroxide solution, and a solution of 2.5 g of calcium chloride (Fluka purum) in 15 ml of deionised water is added. The mixture is stirred for a further 2 hours at a temperature of 70° C. The yellow suspension is then filtered through hard filters, washed with 200 ml of deionised water and dried in vacuo at 100° C. 10.7 g of the calcium salt of the compound of formula (1) are obtained, which colours PVC plastics in greenish-yellow shades.

The complete X-ray diffraction diagram was determined by customary methods with the aid of a Siemens D500 X-ray diffractometer (CuKα radiation).

The X-ray diffraction diagram of the resulting compound corresponds to the β-modification (see Example 1.3).

EXAMPLE 3 Ammonium Salt

Preparation of the diazonium: 5.90 g (20 mmol, 81.5%) of 2-amino-5-nitrobenzene-sulfonic acid sodium/ammonium salt are stirred in 100 ml of deionised water, and 7 ml of an aqueous 37% HCl solution are added. The suspension is then cooled to a temperature of 0-5° C. by means of an ice bath, and 5 ml of a 4N sodium nitrite solution are added dropwise thereto. After 2 hours, 0.5 ml of 1N sulfamic acid is added.

Coupling: 6.2 g (20 mmol) of 3-acetoacetylamino-4-methoxybenzenesulfonic acid sodium salt are dissolved in 200 ml of deionised water. The solution is cooled to a temperature of 0-5° C. and the above diazonium suspension is added dropwise thereto, the pH being maintained at 4.5-5.0 by means of a 30% ammonia solution. When the addition is complete, the reaction mixture is stirred at 0-5° C. for 2 hours and then at room temperature overnight. The mixture is then adjusted to pH 7 by means of a 30% ammonia solution and then stirred at 80° C. for 2 hours. The resulting yellow suspension is filtered by means of hard filters, washed with 100 ml of water and dried in a vacuum cabinet at 90° C. 7.6 g of the ammonium salt of the compound of formula (1) are obtained, which colours PVC plastics in yellow shades.

EXAMPLE 4 Ammonium/calcium Salt Mixture

Preparation of the diazonium: in accordance with the process of Example 3

Coupling: in accordance with the process of Example 3

The mixture is brought to a temperature of 70° C. and a solution of 1.33 g (12 mmol) of calcium chloride in 10 ml of deionised water is added thereto. The pH is then adjusted to 8 by means of a 30% ammonia solution and stirring is then carried out for 2 hours. The resulting yellow suspension is filtered, while hot, through hard filters, washed with 500 ml of deionised water and dried in a vacuum cabinet at 90° C. 8.9 g of the NH₄ ⁺/Ca²⁺ mixed salt of the compound of formula (1) are obtained, which colours PVC plastics in yellow shades.

EXAMPLE 5 Calcium/ammonium Salt Mixture

Preparation of the diazonium: 11.78 g (40 mmol, 81.5%) of 2-amino-5-nitrobenzene-sulfonic acid sodium/ammonium salt are stirred in 200 ml of deionised water, and 14 ml of an aqueous 37% HCl solution are added. The suspension is then cooled to a temperature of 0-5° C. by means of an ice bath, and 10 ml of a 4N sodium nitrite solution are added dropwise thereto. After 2 hours, 0.5 ml of 1N sulfamic acid is added.

Coupling: 12.4 g (40 mmol) of 3-acetoacetylamino-4-methoxybenzenesulfonic acid sodium salt are dissolved in 200 ml of deionised water. The solution is cooled to a temperature of 0-5° C. and the above diazonium suspension is added dropwise thereto, the pH being maintained at 4.5-5.0 by means of a 30% sodium hydroxide solution. When the addition is complete, the reaction mixture is stirred at 0-5° C. for 2 hours and then at room temperature overnight. The mixture is then divided into two portions, each of about 250 ml.

A) The first portion of the above yellow suspension is adjusted to pH 7 by means of a 5% ammonia solution, then stirred for 1 hour and heated to a temperature of 70° C. A solution of 1.8 g (16 mmol) of calcium chloride in 10 ml of deionised water is then added and stirring is carried out for 2 hours. The resulting yellow suspension is filtered by means of hard filters, washed with 1000 ml of hot water and dried in a vacuum cabinet at 90° C. 8.7 g of the calcium salt of the compound of formula (1) are obtained, which colours PVC plastics in yellow shades.

B) The second portion of the above yellow suspension is adjusted to pH 8 by means of a 5% ammonia solution, then stirred for 1 hour and heated to a temperature of 70° C. A solution of 1.2 g (12 mmol) of calcium chloride in 10 ml of deionised water is then added and stirring is carried out for 2 hours. The resulting yellow suspension is filtered by means of hard filters, washed with 1000 ml of hot water and dried in a vacuum cabinet at 90° C. 6.8 g of the calcium/ammonium mixed salt of the compound of formula (1), which contains a little water, are obtained, which colours PVC plastics in yellow shades.

EXAMPLE 6

Preparation of the diazonium: 5.08 g (20 mmol, 92.5%) of 2-amino-5-nitrobenzene-sulfonic acid sodium/ammonium salt are stirred in 100 ml of deionised water, and 7 ml of an aqueous 37% HCl solution are added. The suspension is then cooled to a temperature of 0-5° C. by means of an ice bath, and 5 ml of a 4N sodium nitrite solution are added dropwise thereto. After 2 hours, 0.5 ml of 1N sulfamic acid is added.

Coupling: 6.2 g (20 mmol) of 3-acetoacetylamino-4-methoxybenzenesulfonic acid sodium salt are dissolved in 200 ml of deionised water. The solution is cooled to a temperature of 0-5° C. and a solution of 2.5 g of calcium chloride (22 mmol) in 15 ml of deionised water is added, and the above diazonium suspension is added dropwise thereto, the pH being maintained at 5-6 by means of a sodium hydroxide solution. When the addition is complete, the reaction mixture is stirred at room temperature for 2.5 hours. The mixture is then heated to a temperature of 80° C. and adjusted to pH 8 by means of a 30% sodium hydroxide solution. After being stirred for 1 hour, the mixture is cooled to 50° C. and the resulting yellow suspension is filtered by means of hard filters, washed with 150 ml of water and dried in a vacuum cabinet at 90° C. 9.64 g of the calcium salt of the compound of formula (1), which contains a little water, are obtained, which colours PVC plastics in yellow shades.

EXAMPLE 7 Phase Change

5.0 g of a compound prepared in accordance with Example 1.1) are stirred in 100 ml of isopropanol at a temperature of 80° C. for one hour. The mixture is then cooled to room temperature and the resulting yellow suspension is filtered by means of hard filters, washed with 100 ml of water and dried in a vacuum cabinet at 90° C. 4.5 g of the calcium salt of the compound of formula (1) are obtained, which colours PVC plastics in yellow shades.

The X-ray diffraction diagram of the resulting compound corresponds to the β-modification (see Example 1.3).

EXAMPLE 8 Potassium Salt

Preparation of the diazonium: 5.77 g (20 mmol, 86%) of 2-amino-5-nitrobenzene-sulfonic acid ammonium salt are stirred in 80 ml of deionised water, and 7 ml of an aqueous 37% HCl solution are added. The suspension is then cooled to a temperature of 0-5° C. by means of an ice bath, and 5 ml of a 4N sodium nitrite solution are added dropwise thereto. After 2 hours, 1 ml of a 1N sulfamic acid solution is added.

Coupling: 6.63 g (20 mmol, about 98%) of 3-acetoacetylamino-4-methoxybenzene-sulfonic acid potassium salt are dissolved in 60 ml of deionised water. The solution is cooled to a temperature of 0-5° C. and the above diazonium suspension is added dropwise thereto, the pH being maintained at 4.5-5.0 by means of a 30% potassium hydroxide solution and the viscous suspension being diluted with 50 ml of water. When the addition is complete, the reaction mixture is stirred for 12 hours at room temperature. The suspension is then heated to 75° C. by means of an oil bath and then stirred for 2 hours. The suspension is then filtered by means of hard filters, washed with 400 ml of hot water and dried in a vacuum cabinet at 90° C. 9.1 g of the potassium salt of the compound of formula (1) are obtained, which colours PVC plastics in yellow shades.

EXAMPLE 9 Calcium/potassium Salt Mixture

Preparation of the diazonium: in accordance with Example 5

Coupling: 15.9 g (48 mmol, about 98%) of 3-acetoacetylamino-4-methoxybenzene-sulfonic acid potassium salt are dissolved in 120 ml of deionised water. The solution is cooled to a temperature of 0-5° C. and the above diazonium suspension is added dropwise thereto, the pH being maintained at 4.5-5.0 by means of a 30% sodium hydroxide solution. When the addition is complete, the reaction mixture is brought to room temperature and then stirred for 12 hours.

Half the yellow suspension is then heated to 70° C. by means of an oil bath; a solution of 2.5 g of calcium chloride in 10 ml of water is added and stirring is then carried out for 2 hours. The resulting yellow suspension is filtered by means of hard filters, washed with 1 litre of hot water and dried in a vacuum cabinet at 90° C. 9.4 g of the calcium/potassium mixed salt of the compound of formula (1) are obtained, which colours PVC plastics in yellow shades. 

1. A monoazo compound of formula

which is present in the form of a mono-, di-, tri- or tetra-valent mixed salt of different cations, such as, for example, Ca²⁺, Na⁺, NH₄ ⁺, NR₄ ⁺, H⁺, Li⁺, K⁺, Mg²⁺, Ba²⁺, Sr²⁺, Al³⁺, Pb²⁺, Mn²⁺, Zn²⁺, Cr²⁺, Co²⁺, Fe²⁺, Fe³⁺, Zr⁴⁺ and Cu²⁺ wherein R is C₁-C₆alkyl, in a freely selected ratio.
 2. The calcium salt of the monoazo compound of formula

which has two crystal polymorph forms—a somewhat reddish yellow as α-modification and a greenish yellow as β-modification—having different properties.
 3. A Ca²⁺/Na⁺ mixed salt of the monoazo compound of formula (1) according to claim
 1. 4. A Ca²⁺/NH₄ ⁺ mixed salt of the monoazo compound of formula (1) according to claim
 1. 5. A Ca²⁺/K⁺ mixed salt of the monoazo compound of formula (1) according to claim
 1. 6. A greenish β-modification of the calcium salt of the monoazo compound of formula (1) according to claim
 2. 7. A process for the preparation of a monoazo compound of formula (1) according to either claim 1 or claim 2, which comprises diazotisation of 2-amino-5-nitrobenzene-sulfonic acid or a salt or a mixed salt thereof, and coupling to 3-acetoacetylamino-4-methoxybenzenesulfonic acid/salt.
 8. A method of mass-pigmenting high molecular weight organic material, which comprises incorporating into such material a monoazo compound of formula (1) according to either claim 1 or claim
 2. 9. Use of a monoazo compound according to either claim 1 or claim 2 in the mass-pigmenting of organic material.
 10. Use of a monoazo compound according to either claim 1 or claim 2 in the production of solid toners, wax transfer ribbons or colour filters. 